Assume $600 average rent, so living in IHS
Housing (assuming $200 rent) saves you $400/month
Please note, not all IHS housing is $200 per month, it may be more depending on
location.
I assume you only rent for 2 years and then you buy a house after that.

Assume that you would have to invest $23,808
per year with a"balanced
portfolio" of investements
(http://cgi.money.cnn.com/tools/retirementplanner/retirementplanner.jsp)
and $14,000 per year of Soc. Sec. benefits to achieve $84,167 per year during
retirement.